Browse Promo

Browse Deals

Buckling bridges

Study calls for costly repair or replacement of downtown spans

Last year, the Montana Department of Transportation classified the Madison Street and Higgins Avenue bridges in downtown Missoula as being structurally deficient. Now, after a year of study, public comment and input from the city, MDT has recommended two options for the deteriorating structures: major rehabilitation or total bridge replacement. How it will pay for either remains up in the air.

MDT prefers to rehabilitate the bridges, and Bridge Bureau Chief Kent Barnes says he’d be “very surprised” if this option doesn’t prove to be the most feasible, most affordable and best suited to meet users’ needs.

“What would really drive us toward [bridge replacement] at this point,” Barnes says, “is if we get in there and we start looking at the structural rehabilitation and we start recognizing that there’s more problems with the structure than we believe there is.”

click to enlarge

Grace Ryan

The Montana Department of Transportation suggests a major rehabilitation of the “structurally deficient” Madison Street and Higgins Avenue bridges in order to stabilize the deteriorating structures while also increasing bike and pedestrian access.

The known structural problems with the spans, which connect downtown to the Hip Strip and the University of Montana, are outlined in the Missoula Bridges Planning Study, which the department released earlier this month. The study describes “several forms of deterioration,” including cracked concrete decking, corroded steel and leaking joints in the deck. As a result, the study ranks the bridges “poor for structure condition and deck condition.” It also describes the steel-and-concrete structures as “vulnerable” to seismic activity. In addition, the bridges fail to meet current needs.

“When we talk about major rehabilitation, there’s really two goals here,” Barnes says. “One goal is to rehabilitate and preserve the structure. The other goal is to reconfigure the bridge deck and widen it as best we can to meet the needs and desires for increasing pedestrian and bike access across the bridge.”

Barnes explains that meeting those goals means finding a way to repair the bridges’ existing problems, slow future deterioration, preserve the existing four lanes of traffic and expand the width of bike lanes and sidewalks—all without exceeding the bridges’ existing foundation capacity. It’s no easy task considering the decks of both bridges are already crowded. The challenge for engineers is to find ways to make more room without adding too much weight and overloading the existing spans. That will likely mean removing medians, narrowing traffic lanes and widening the decks to the extent possible.

In order to determine exactly if—and if so, how—the bridges can be rehabilitated, MDT must conduct a structural analysis, which will take money currently not budgeted. MDT plans to rely primarily on the federal Highway Trust Fund to initiate and complete the project, but that fund is projected to be completely depleted this summer. Until a new transportation spending plan is signed into law, the MDT can’t proceed. The planning study estimates work on the rehabilitation project will begin within one to five years. The funding uncertainty, though, means “one year is drifting away very quickly,” Barnes says.

The total cost of major rehabilitation is projected to be $4 million–$8 million for the Higgins bridge and $2 million–$5 million for Madison. According to the study, that would buy approximately 25 to 50 more years for each structure. It’s not a permanent solution, but Barnes thinks it’s for the best.

“Where is Missoula going with the whole transportation network?” he asks. “Some of the traffic studies right now say that what we should be doing with Madison and Higgins is expanding them to three lanes each direction.”

One such study predicts annual average daily traffic on the Higgins bridge will go from 18,148 vehicles in 2010 to 23,578 in 2040. Traffic on the Madison bridge is projected to almost double over that 30-year period, rising from 12,685 vehicles a day to 22,411. As a result of such data, MDT did consider an option for replacing the current spans with six-lane bridges. While such a plan was rejected, it remains a future option.

“It could be that in 30 years, there is a pattern change that we have to expand those bridges out to support higher actual traffic lanes,” Barnes says.

Ellen Buchanan, director of the Missoula Redevelopment Agency, says she and others in city government acknowledge the possibility of increased downtown traffic, but she has a different vision of how best to manage that growth. Instead of larger bridges that would disrupt downtown’s character, she floats the idea of an electric streetcar crossing the Madison bridge and combating the rising traffic patterns. She also says additional one- or two-lane bridges could be added to the downtown area to meet demand.

“Traditionally in the United States our traffic engineering answer to congestion has been to make streets wider,” Buchanan says. “The thinking now is slowly but surely shifting to maybe you just expand the network, you disperse the traffic over more streets instead of making three streets so wide no one wants to be on them. That same thinking could apply to a bridge.”

In the meantime, work on the Higgins and Madison bridges will have to wait until Congress and the Obama administration agree on a way to increase revenue for the Highway Trust Fund, which currently relies on the federal 18.4 cents-per-gallon gas tax. Proposals include closing corporate tax loopholes, adding tolls to more highways and raising the federal gas tax for the first time since 1993.